This project involves studies of 40 children diagnosed as having infantile autism according to DSM-III (1980) criteria, ages 2 to 7 years. The main objectives are (1) to assess critically and objectively the effects of haloperidol on behavioral symptoms, on learning, and, in a prespective fashion, its effects on the development of neurological neuroleptic-induced movements. Learning will be evaluated with the use of an automated data collection system. Blood levels of haloperidol and of prolactin will also be assessed and related to behavioral outcome as well as to the development of neurological neuroleptic-induced movements. The study is double-blind and placebo controlled. It consists of 2 phases: a short-term (14 weeks) and a long-term phase (up to 3 years). In the short-term phase a within groups and a between groups comparison is used. In the long-term phase, subjects will be randomly assigned to continuous and intermittent haloperidol maintenance periods of 6 months followed by periods of 4 weeks on placebo. An additional sample (approximately 30) autistic children of same ages will be studied continuously for long term effects and added to this sample for data analyses. This project is a major contribution in assessing the short and long-term safety of haloperidol in autistic children; and its effects on learning and on behavioral symptoms. It also has relevance for other types of populations of children treated with neuroleptics including those who are mentally-retarded. This is a prospective project to study neurological neuroleptic-induced movements in a population who have such a high rate baseline of non-drug induced abnormal movements.